The present disclosure generally relates to testing and evaluation of subterranean formations and formation fluids and, more particularly, to systems and methods for making optimized borehole acoustic measurements.
It is well known in the subterranean well drilling and completion art to perform tests on formations penetrated by a wellbore. Such tests are typically performed in order to determine geological or other physical properties of the formation and fluids contained therein. Measurements of parameters of the geological formation are typically performed using many devices including downhole formation tester tools. In certain applications, the tools may be used for logging-while-drilling (LWD) or measurement-while drilling (MWD) purposes.
Acoustic tools are commonly employed in geophysical surveys to investigate mechanical properties of the borehole and formation. This is accomplished by measuring the velocity, or equivalently slowness, of wave propagation for different acoustic modes and relating these slowness values to material properties. Acoustic tools that are currently in use generally employ uniformly spaced sensors. In other cases, sensors may be located in discrete blocks or sub-arrays, but sensors within these discrete blocks are designed to be uniformly spaced. The uniform spacing between the sensors leads to the generation of aliases—replicas of the real slowness values of the waveform, occurring because the limited spatial information obtained from the sensors does not lead to a unique solution.
Increasing the number of receivers alleviates the problem, but introduces additional cost, fabrication challenges, and computational inefficiencies in processing due to increased amount of data. Additionally, time semblance based methods typically used to determine slowness from sensor data are designed for uniform spacing, limiting the design alternatives for the sensor placement. What is needed is a system and method to provide stable and accurate measurements of slowness values, creating cleaner semblance images and reducing aliasing, without requiring additional cost, fabrication challenges and computational inefficiencies.
While embodiments of this disclosure have been depicted and described and are defined by reference to exemplary embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.